963 votesBanban Daudau commented
"Edit: Just to put the value of this into context, I've just run some stats on the Adobe breach. Of the the 152,989,508 rows in the dump, only 49,905 email addresses have a "+" in the address so that's 0.03% of entries. That number is also a bit high as it includes junk entries. I'm definitely not ruling this idea out - it's still planned - I just wanted to give a sense of how useful it would be."
I guess running those stats took way more work as a simple implementation (removing the +... part before running the db search seach for '+%'). Also did you check if the adobe breach was a good choice to run this stat ? If I'm not wrong the + feature started to happen in 2002 and most of adobe account were created before this time (I really may be wrong, please verify).